This invention relates to a necking-out tool for forming cylindrical nipples ("necks") on the circumferential surface of pipelines, containers and the like. The tool includes a screw plug having a hook-shaped forming head and a thrust sleeve fitted with a coaxial downholder cooperating with the forming head and the screw plug, and having a hollow cylindrical interior corresponding to the forming head for the reception of the formed neck.
When such a tool is used, a hole is first drilled into the cylindrical hollow body that is to be provided with the nipple ("neck"), the diameter of the hole just permitting the forming head of the tool to be passed through. For this purpose, the forming head is turned far enough out of the thrust sleeve to enable it to be manipulated through the hole by taking advantage of an oblique slot cut into the head. The tool is then reerected into a radical position in relation to the pipe axis and the forming head is retracted into the thrust sleeve by rotating the screw plug. This operation causes the material of the hollow body to be plastically deformed into the shape of a projecting edge having an external diameter corresponding to the internal diameter of the thrust sleeve. During this forming process, the thrust sleeve bears on the hollow body which takes up the reactive force. A tool of this type and the manner in which it functions is described in German Patent No. 7 311 408.
This prior art tool is generally used by simply mounting it on the hollow body that is to be deformed and by then bringing about the desired forming operation by rotating the screw plug. The hollow body is not gripped or embraced by an accessory appliance. During manipulation of the prior art tool, it occasionally happens that during the final phase of the forming operation the forming head pulls out of the hollow body so that the necking-out operation cannot be completed and the pipe which is to be joined to the hollow body will not then fit the nipple, respectively neck.
The sudden release of the forming head is also a considerable accident hazard, particularly when the fitter is in a position in which he has restricted freedom of movement. The thrust sleeve must be tightly held by hand during the entire operation and this may also be very difficult in an inaccesible place, since a fairly considerably physical effort is needed, which may be beyond the strength of some men. The necking-out operation may then take some time to perform.
It has been proposed in U.S. Pat. No. 3,131,746 to design a necking-out tool in the form of a massive body which can be hingeably opened and placed and screwed around the pipeline on which a neck is to be formed. A heavy body of such a kind is needed principally because the forming head is not symmetrical and therefore subjected to a one-sided load. It is often impossible to attach this massive body to pipelines that are already installed. Its major drawback is that it is suitable for application to pipes of only one particular diameter. A plumber who wishes to form necks on pipes of different diameters would thus be obliged to carry a corresponding number of tools of this kind in his kit. However, in view of their weight this would be a practical impossibility. Consequently, this prior art tool is primarily intended for use inside the factory and is not practical for a small plumber's business or for use on building sites.